Method of manufacturing a monolithic ceramic electronic device

ABSTRACT

A method of manufacturing a monolithic ceramic electronic device includes the following steps: forming a first metal film on a PET film; forming a multilayered metal film by forming a second metal film on a part of the first metal film, the second metal film being thicker than the first metal film; forming a monolithic ceramic structure including the multilayered metal film; forming the first metal film, which is partially overlain by the second metal film in the monolithic ceramic structure, into an insulating structure in such a manner that metal components forming the first metal film are diffused into the ceramics; and firing the ceramics. Disclosed also is a monolithic ceramic electronic device manufactured by the method. As a result, a stepped portion between a portion in which the internal electrodes overlap one another and a portion in which the internal electrodes do not overlap can be prevented from being formed, and delamination can effectively be prevented, whereby a monolithic ceramic electronic device exhibiting stable characteristics and a method for manufacturing the monolithic ceramic electronic device can be obtained.

This is a Division of application Ser. No. 08/617/177, filed Mar. 18,1996, now U.S. Pat. No. 5,769,985, issued on Jun. 23, 1998.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electronic part and a method ofmanufacturing same, and more particularly to a monolithic ceramicelectronic device and a method of manufacturing same.

The present invention can be adapted to a variety of electronic devices,e.g. a monolithic capacitor, a monolithic piezoelectric device or amultilayered ceramic substrate, and a method of manufacturing suchdevices.

2. Related Background Art

Methods are known of integrally firing metal elements and ceramicelements for manufacturing a monolithic ceramic electronic device, suchas a monolithic capacitor, having internal electrodes.

For example, a pattern made of conductive paste is printed on a ceramicgreen sheet to form internal electrodes. Then, a plurality of theceramic green sheets each having the internal electrodes are laminated,and then an appropriate number of ceramic green sheets having nointernal electrodes are laminated on both sides of the stack of greensheets to form a monolithic ceramic structure. Alternatively,predetermined patterns of ceramic paste and conductive paste may besequentially printed to form a monolithic ceramic structure.

Then, the monolithic ceramic structure is pressed in a direction of itsthickness so that the ceramic layers are brought into tight contact witheach other. Further, the monolithic ceramic structure is fired to obtaina sintered structure. Appropriate external electrodes are formed on theouter surface of the sintered structure to produce a monolithic ceramicelectronic part.

In recent years it has been required to reduce the sizes of electronicparts, as well as the sizes and thicknesses of monolithic ceramicelectronic devices. When the monolithic ceramic electronic device isintended to be reduced in size and thickness, the ceramic layers, eachof which is held between the internal electrodes, are required to bemade thinner. Accordingly, thinner green sheets are required when themonolithic ceramic structure is manufactured.

However, it is difficult to handle excessively thin ceramic greensheets. Moreover, the portions including the internal electrodes, whichoverlap one another, are thicker than the portions not includinginternal electrode in a monolithic ceramic structure. As a result, stepshave been inevitably formed between these portions.

In particular, since the steps are formed when the monolithic ceramicstructure is pressed in the direction of its thickness prior to thefiring process, the pressure is mainly applied onto the portions wherethe internal electrodes overlap one another. Accordingly, the pressureis insufficient in the other portions. As a result, there is apossibility that a layer-separating phenomenon called delamination mayoccur. Also, there is a possibility that solvent in the ceramic greensheet may cause the internal electrodes to be swelled. If that occurs,the internal electrodes cannot accurately be formed into desired shapes.

Therefore, it has been extremely difficult to reduce the thickness of aceramic green sheet to about 6 μm or thinner.

Such problems may arise in making a monolithic ceramic structure inwhich ceramic paste and conductive paste are alternately laminated.

To overcome these problems, a method has been suggested in which a metalfilm, formed by a thin film forming method, is used as the internalelectrodes, the method being exemplified by the following first to thirdmethods.

The first method, shown in FIG. 1, begins with the step of forming ametal film over the entire surface of a supporting member 1 by using athin film forming method, such as a sputtering method. Then, a resistlayer having openings corresponding to the shapes of the electrodes isformed on the metal film, and then the metal film is patterned byphotolithography. Thus, a metal film 2 is formed as shown in FIG. 1.Then, a ceramic green sheet 3 is formed on the metal film 2. Byrepeating the steps of forming the metal film 2 and forming the ceramicgreen sheet 3, a monolithic structure 4 is formed.

In the second method, which is disclosed in JP-A-64-42809, a ceramicgreen sheet is formed on a first film made of synthetic resin; and ametal film is formed on a second supporting film by a thin film formingmethod. Then, the metal film supported by the second supporting film istransferred to the ceramic green sheet on the first supporting film sothat the green sheet has the metal film thereon. A monolithic ceramicstructure is obtained by laminating a plurality of such green sheets.

The third method begins with the step of forming a metal film on theentire surface of a supporting film by a thin film forming method. Then,the metal film is patterned by a photolithography method. Next, aceramic green sheet is formed on the supporting film having thepatterned metal film thereon so that the green sheet is combined withthe metal film. Then, the green sheet supported by the supporting filmis transferred onto a substrate by using a thermal transfer method sothat a monolithic ceramic structure is obtained.

The first to third methods, in each of which metal films formed by athin film forming method are used as the internal electrodes, are ableto make the internal electrodes thinner as compared with the method offorming the internal electrodes by using conductive paste.

However, past attempts to make each layer thinner have resulted in anincrease in the number of laminated layers, thus causing the internalelectrodes to be thickened in comparison with the thickness of theceramic layer held between the internal electrodes. As a result, asshown in FIG. 2, the first method results in a difference in thicknessbetween a portion 6, in which only the ceramic green sheets arelaminated, and a portion 7, in which internal electrodes 8 overlap oneanother. Therefore, when the laminated structure is pressed in thedirection of its thickness, the pressure is primarily applied only tothe portion in which the internal electrodes 8 overlap one another.Thus, the strength of adhesion between the ceramic layers may be reducedin the region 6 in which the internal electrodes do not overlap. As aresult, delamination may easily take place when the laminated structureis sintered.

Moreover, the first method requires further process steps after themetal film has been formed on the supporting member, such as a step offorming patterns of a resist layer, a step of etching the pattern and astep of stripping the resist layer off.

The second method also encounters the problem of thickening of theportion in which the internal electrodes overlap one another, ascompared with the region having no internal electrodes. Therefore, thesecond method also may suffer from the delamination problem. Further, inthe case where the ceramic green sheets are made extremely thin, itwould be difficult to handle such green sheets. Moreover, it would bedifficult to position the metal film on a green sheet with high accuracybecause a transferring process is involved.

And, in the transferring process, the ceramic green sheet must bebrought into contact with the second supporting film in order to makethe portion having no metal film. The second supporting film must bestripped from the green sheet having the metal film after thetransferring process. Therefore, both the metal film and the ceramicgreen sheet must be able to be easily stripped from the secondsupporting film. However, this requirement can not easily be satisfied.Thus, there is a possibility that a portion of a ceramic green sheet maybe destroyed when stripping off the second supporting film.

Since the third method has the steps of forming the metal film by thethin film forming method and then performing the patterning process bythe photolithography method, this manufacturing process tends to becomecomplicated. Moreover, making the structure in which the metal film andthe ceramic green sheet are in contact with the supporting film requiresboth the metal film and the ceramic green sheet to be easily strippedfrom the supporting film when transference from the supporting film isperformed. However, this requirement cannot easily be satisfied.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a methodof manufacturing a monolithic ceramic electronic device which is capableof preventing occurrence of a difference in thickness between a regionin a monolithic ceramic structure in which internal electrodes areformed, and a region in which the internal electrodes are not formed,and is therefore capable of effectively preventing delamination.

A further object is to provide a method which is capable ofmanufacturing a monolithic ceramic electronic device more simply andstably than the conventional methods of manufacturing the monolithicceramic electronic device which have included a step of forming theinternal electrodes by a thin film forming method.

To achieve these objects, according to one aspect of the presentinvention, there is provided a method of manufacturing a monolithicceramic electronic device, including the steps of: forming a first metalfilm on a first supporting member by a thin film forming method;forming, on the first metal film, a resist layer having pattern holestherein; forming second metal films thicker than the first metal filmwithin the pattern holes formed in the resist layer; forming amonolithic ceramic structure including the resist layer and the firstand second metal films; and firing the monolithic ceramic structure tochange the first metal film into an insulating material and to removethe resist layer.

According to another aspect of the present invention, the step offorming the monolithic ceramic structure includes the steps of forming aceramic green sheet on a second supporting member; and separating themonolithic ceramic structure from the first supporting member whileseparating the ceramic green sheet from the second supporting member,and alternately stacking, on a laminating stage, the monolithic ceramicstructure and the ceramic green sheet.

According to a further aspect of the present invention, the step offorming the monolithic ceramic structure includes the steps of forming aceramic green sheet on a second supporting member; transferring, ontothe ceramic green sheet, the monolithic ceramic structure on the firstsupporting member to form a green sheet including a metal film; andsequentially transferring and stacking a plurality of the green sheetseach having the metal film and thereby forming the monolithic ceramicstructure.

It is preferable that transference of the metal film be performed byusing a roll press in the step of forming the green sheet having themetal film by the transferring method, so as to enable a thin metal filmto be easily and smoothly transferred to the ceramic green sheet.

According to these aspects of the present invention, the first metalfilm is thinner than the second metal film. The thickness ispredetermined such that the first metal film can be formed into aninsulating material or structure during firing. The process forconverting the first metal film into the insulating material can berealized by diffusion of the metal composing the metal film into thesurrounding ceramics, the metal being diffused in the form of oxideions. The predetermined thickness with which the first metal film isformed into the insulating structure cannot be determined definitely,because the thickness varies depending upon the material composing thefirst metal film and the firing conditions including the firingtemperature. However, it is preferable that the thickness be 0.1 μm orthinner. As a result, the first metal film can reliably be formed intothe insulating structure.

The resist layer is mainly composed of resist resin which disappearswhen fired. Since the resist layer disappears when the firing process isperformed, a process of stripping off the resist layer is not requiredin the present invention. Moreover, in the firing process, surroundingceramics are moved into the portion from which the resist layer hasdisappeared. Therefore, a problem of generation of voids can beprevented.

Preferably, inorganic components are added to the resist. The inorganiccomponents are composed of inorganic materials, such as ceramics orglass, which do not disappear after firing. Thus, the inorganiccomponents have a function of preventing reduction of the strength ofthe portion from which the resist layer has disappeared. In the casewhere the inorganic components are contained in the resist layer, thesurrounding ceramics move smoothly into the portion from which theresist resin has disappeared due to firing. As a result, the compositionof the ceramics in the sintered body is homogeneous over the entiresintered body. Therefore, the structure, in which the inorganiccomponents are contained in the resist layer, enables a further uniformand dense sintered structure to be obtained.

The materials of the first and second metal films are not limitedparticularly. According to an aspect of the present invention, the firstmetal film contains Cu and the second metal film contains Ni. The firstmetal film containing Cu can easily be changed into oxides to form theinsulating structure after firing. By forming the second metal film withNi, the cost of the internal electrodes can be reduced.

According to a further aspect of the present invention, there isprovided a method of manufacturing a monolithic ceramic electronic partcomprising the steps of: forming a first metal film on a firstsupporting member by a thin film forming method; forming a multilayeredmetal film by forming a second metal film on a part of the first metalfilm by the thin film forming method, the second metal film beingthicker than the first metal film; forming a monolithic ceramicstructure incorporating the multilayered metal film; and forming aportion of the first metal film, which is not overlain by the secondmetal film in the monolithic ceramic structure, into an insulatingstructure by causing the metal components forming the portion to diffuseinto the ceramics, in conjunction with firing the ceramics.

According to a still further aspect of the present invention, thethickness of the first metal film is about 100 nm or thinner and thethickness of the second metal film is at least about 300 nm and at mostabout 1000 nm. The reason for this is that the first metal film must bestructured in such a manner that the portion of the first metal film,which is not located below the second metal film, is required to bechanged into the insulating structure when the ceramics are fired. Thatis, the thickness of the first metal film is 100 nm or less so that themetal components composing the first metal film can easily be diffusedinto the ceramics due to firing in such a manner that the metalcomponents are in the form of oxide ions when diffused. The reason whythe thickness of the second metal film is at least 300 nm is thatoxidation of the second metal film is prevented when the first metalfilm portion is changed into the insulating structure. That is, thesecond metal film serves as the internal electrodes. Note that the upperlimit on the thickness of the second metal film is not limitedparticularly. However, to use the second metal film as the internalelectrodes of a monolithic ceramic electronic device and to achieve themain object of the present invention, which is to prevent generation ofa stepped portion, the thickness is usually determined to be at most1000 nm.

According to one aspect of the present invention, the step of convertingthe part of the first metal film into the insulating structure andfiring the ceramics is performed by firing the monolithic ceramicstructure under a partial pressure of oxygen at which the first metalfilm is oxidized but the second metal film is not oxidized. That is,control of the partial pressure of oxygen to that level enables thefirst metal film to be oxidized at the time of firing the ceramics, andthe first metal film portion, which is not located below the secondmetal film, to be converted into the insulating structure, and preventsoxidation of the second metal film. The level of the partial pressure ofoxygen can be determined appropriately and easily adapted to differentmaterials and to the thicknesses of the first and second metal films andtemperature and time for which the firing process is performed.

The step of forming the multilayered metal film can be performed by anappropriate photolithography method. For example, the step of formingthe multilayered metal film has the steps of forming, on the first metalfilm, a resist layer having pattern holes therein; forming, in thepattern holes in the resist layer, second metal films each of which isthicker than the first metal film by the thin film forming method; andstripping the resist layer.

Also, the step of forming the monolithic ceramic structure including themultilayered metal film can be realized by a conventional transferencemethod. According to an aspect of the present invention, the step offorming the monolithic ceramic structure has the steps of forming agreen sheet including a metal film by forming a ceramic green sheet onthe multilayered metal film; and stacking a plurality of such greensheets. According to another aspect of the present invention, the stepof forming the monolithic ceramic structure is realized by atransferring method having the steps of forming a ceramic green sheet ona second supporting member; forming a green sheet including a metal filmby transferring, to the ceramic green sheet, the multilayered metal filmsupported by the first supporting member; and forming the monolithicceramic structure by sequentially transferring a plurality of the greensheets each having a metal film. When the transferring method isemployed, it is preferable that a roll press be used to transfer themultilayered metal film to the ceramic green sheet.

In the present invention, the first metal film is formed, and then theresist layer is formed. Then, the second metal films are formed withinthe pattern holes in the resist layer so that a laminated memberincluding a metal-layer and a resist-layer is formed. Therefore, nooperations, such as etching and stripping of the resist layer, arerequired to be performed. That is, the step of etching the first metalfilm and the step of stripping the resist can be omitted. Therefore, thetime required to process the metal film formed by the thin film formingmethod can significantly be shortened. Moreover, the incidence ofdefective parts can be lowered, such incidents often being due to theprocess of washing off the etching liquid. Since the resist is notrequired to have etching resistance, resin for forming the resist may beselected from a wide variety of materials. Thus, the cost of thematerial can be reduced.

Moreover, in the step of firing the monolithic ceramic structureincluding a laminated member having a metal layer and a resist layer,the resist layer is stripped and the first metal film is converted intothe insulating structure at the same time the ceramics are fired.Therefore, no additional process is required to easily and stably obtaina sintered structure for a monolithic ceramic electronic device in whichinternal electrodes formed by the second metal film are stacked.

The first metal film formed on the overall surface enables the size ofthe stepped portion, between the portion in which the internalelectrodes overlap one another, and the portion in which the internalelectrodes do not overlap, to be reduced. As a result, generation ofdelamination can be prevented satisfactorily.

In the case where the step of forming the monolithic ceramic structureconsists of the step of forming the ceramic green sheet on the secondsupporting member; and the step of alternately stacking, on the stackingstage, a laminated member having the metal-layer and resist-layersupported on the first supporting member and the ceramic green sheetsupported by the second supporting member, a sole member is strippedfrom each supporting member. That is, the first metal film is strippedfrom the first supporting member and the green sheet is stripped fromthe second supporting member. Therefore, the force required to stripeach member can easily be controlled.

In the case where the step of forming the monolithic ceramic structureis performed by the transferring method, that is, in the case where theceramic green sheet is previously formed on the second supportingmember, and then a laminated member having metal layers and resistlayers is transferred to the ceramic green sheet to form the green sheetintegrally having the metal film, only the ceramic green sheet isstripped from the supporting member when the stacking process isperformed. Therefore, the force required to strip the ceramic greensheet off of the supporting member can easily and reliably be controlledby using an appropriate release layer. As a result, by using thetransference method, a ceramic green sheet and electrode material thatis even thinner than previously may be employed to manufacture amonolithic ceramic electronic device. Moreover, delamination whichoccurs due to defective stacking and/or defective pressing can beprevented.

As a result, according to the present invention, if the thickness of amonolithic ceramic electronic device to be manufactured is intended tobe reduced and the number of stacked internal electrode layers of thesame is intended to be increased, the incidence of defective parts dueto delamination can be lowered. Moreover, monolithic ceramic electronicdevices can stably be supplied with a simple process.

The method of manufacturing the monolithic ceramic electronic deviceaccording to the present invention, including the step of forming thefirst metal film on the entire surface of the first support layer,enables the size of the stepped portion, between the region in which theinternal electrodes overlap one another (the region in which the secondmetal films overlap one another), and the region in which the internalelectrodes do not overlap, to be reduced. As a result, delamination inthe obtained sintered structure can effectively be prevented.

Moreover, the first metal film is converted into the insulatingstructure in the process of firing the ceramics. Therefore, the firstmetal film which is formed to reduce the size of the stepped portiondoes not act as a conductor. As a result, even if the first metal filmis formed, short circuits and the like do not occur. Moreover, thenecessity of partially stripping the first metal film in the followingstep by etching or the like can be eliminated. Therefore, an additionalprocess for forming a multilayered metal film is not required.

The first metal film is in the form of oxide ions, diffused into theceramics. By controlling the composition of the first metal film, thecomposition of the ceramics can be controlled. Therefore, a monolithicceramic electronic device exhibiting desired characteristics can beprovided.

The multilayered metal film is supported by the supporting member. Inthis state, only the first metal film is in contact with the supportingmember. Therefore, the stripping force required to strip themultilayered metal film off the supporting member is easily determinablewith an appropriate release layer. Therefore, the stripping forcerequired to remove the first metal film from the supporting member caneasily be determined. As a result, in an exemplary case where themultilayered metal film is transferred to the ceramic green sheet formedon the second supporting member, the multilayered metal film can easilybe stripped from the supporting member. Since the second supportingmember is in contact with only the ceramic green sheet, the secondsupporting member is required to be stripped easily and smoothly fromthe ceramic green sheet. Therefore, the second supporting member isrequired to have a simple stripping characteristic.

The present invention may be adapted to any of a variety of methods ofmanufacturing a monolithic ceramic electronic device of a type includinginternal electrodes, such as a monolithic capacitor, a ceramic-laminatedpiezoelectric part and a multilayered ceramic substrate.

Other objects, features and advantages of the invention will be evidentfrom the following detailed description of the preferred embodimentsdescribed in conjunction with the attached figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view showing a conventional method ofmanufacturing a monolithic capacitor;

FIG. 2 is a cross sectional view showing a monolithic ceramic structurein a conventional monolithic capacitor;

FIGS. 3A and 3B are cross sectional views respectively showing a step offorming a first metal film on a first supporting member according to afirst embodiment of the invention and a step of forming a resist layerand a second metal film;

FIG. 4 is a cross sectional view showing a step of forming a ceramicgreen sheet on a second supporting member;

FIG. 5 is a cross sectional view showing a monolithic structure beforeit is fired;

FIG. 6 is a horizontal cross sectional view showing a sintered structureobtained by firing a monolithic chip;

FIG. 7 is a schematic cross sectional view showing a monolithiccapacitor obtained according to the first embodiment;

FIG. 8 is a cross sectional view showing a step of forming a first metalfilm on a first supporting member according to a fourth embodiment ofthe invention;

FIG. 9 is a cross sectional view showing a step of forming a resistlayer having pattern holes on the first metal film;

FIG. 10 is a cross sectional view showing a step of forming a secondmetal films within the pattern holes in the resist layer;

FIG. 11 is a partially-cut cross sectional view showing a process forforming a metal sheet integrally having a green sheet by using a rollpress;

FIG. 12 is a cross sectional view showing a laminated structure;

FIGS. 13A and 13B are cross sectional views respectively showing a stepof forming a first metal film and a step of forming second metal filmsin pattern holes in a resist;

FIG. 14 is a cross sectional view showing a step of forming amultilayered metal film on a supporting member;

FIG. 15 is a cross sectional view showing a step of forming a greensheet integrally having the metal film by molding a ceramic green sheeton the multilayered metal film;

FIG. 16 is a cross sectional view showing a monolithic ceramicstructure;

FIG. 17 is a cross sectional view showing a sintered structure;

FIG. 18 is a cross sectional view showing a monolithic capacitor;

FIG. 19 is a cross sectional view showing a step of forming a ceramicgreen sheet on a second supporting member according to an eighthembodiment of the invention;

FIG. 20 is a cross sectional view showing a step of forming amultilayered metal film;

FIG. 21 is a cross sectional view showing a process for transferring amultilayered metal film to a ceramic green sheet by the method accordingto the eighth embodiment; and

FIG. 22 is a cross sectional view showing a green sheet integrallyhaving the metal film obtained according to the eighth embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Referring to the drawings, preferred embodiments of the presentinvention will now be described.

First Embodiment

As shown in FIG. 3(a), a polyethylene terephthalate film serving as afirst supporting member 11 is coated with silicon resin (not shown).Then, a first metal film 12 is formed over the entire surface of thefirst supporting member 11. The first metal film 12 is an Ag layerhaving a thickness of 0.1 μm and is formed by an evaporation method.

Then, a resist layer is formed on the first metal layer 12 by applying aresist having a thickness of 0.8 μm. The resist, whose main componentsare quinone and diazide formalin resin, contains 10 vol % of BaTiO₃powder.

Then, an exposing process and a developing process are performed, toobtain a resist layer 13 having pattern holes 13a formed therein asshown in FIG. 3(b).

Next, second metal films 14 are formed on the first metal film 12 in theregions within the pattern holes 13a formed in the resist layer 13. Thesecond metal films 14 are formed by applying Pd to have a thickness of0.8 μm by electroplating. The second metal films 14 form internalelectrodes to be described later.

On the other hand, a polyethylene terephthalate film is prepared as asecond supporting member 15 as shown in FIG. 4. Then, ceramic slurrywhose main component is BaTiO₃ is formed into a sheet on thepolyethylene terephthalate film 15 to have a thickness of 6 μm so that aceramic green sheet 16 is obtained.

Then, a plurality of laminated members 17 having metal layers 14 andresist layers 13 as shown in FIG. 3(b) are alternately laminated withthe ceramic green sheets 16 so that a monolithic structure is obtained.The monolithic structure is obtained by stacking a laminated member 17,while supported by the polyethylene terephthalate film serving as thefirst supporting member 11, on the ceramic green sheet 16. This is doneby placing the upper side of the monolithic structure 17, i.e. the sideon which the second metal layers 14 are coated, in contact with theceramic green sheet 16; and then pressing the monolithic structure, atabout 80° C.; and then stripping off the first supporting member 11.Then, similar heat pressing steps are performed so that the ceramicgreen sheets 16 and laminated members 17 are sequentially laminated.Thus, a laminated member 18 shown in FIG. 5 can be obtained.

The laminated member 18 is cut in the direction of its thickness toobtain predetermined monolithic chips for monolithic capacitors. Then,the obtained monolithic chips are fired at 1300° C. in air. As a result,a sintered member 19 shown in FIG. 6 can be obtained. In the sinteredmember 19, internal electrodes 20, each of which is formed by a secondmetal film 14, overlap one another.

Note that the first metal film 12 is heated in the firing process so asto change it into an insulating material. In the resist layer, resistresin has disappeared during the firing process. On the other hand,ceramic powder contained in the resist layer and ceramic that has movedfrom the peripheral region of the resist layer form a dense sinteredstructure similarly to the sintered portions where no resist wasinitially present. As a result, the internal electrodes 20 aresurrounded by dense ceramics, as shown in FIG. 6.

On the outer surface of the sintered structure obtained as describedabove, external electrodes 21a and 21b as shown in FIG. 7 are applied.Thus, a monolithic capacitor 22 is obtained. Note that FIG. 6 shows across section taken along line X--X of the sintered structure shown inFIG. 7.

The structure of the monolithic capacitor 22 that was obtained wasobserved by cutting in the direction X--X shown in FIG. 7. It was seenthat stepped portions, between the portions in which the internalelectrodes overlap one another, and the portions in which the internalelectrodes do not overlap, were decreased as compared with theconventional monolithic capacitor.

The electrical characteristics of the monolithic capacitor weremeasured. It was seen that the desired design characteristics wereobtained. In this measurement, no delamination was seen in the sinteredstructure.

The characteristics of a monolithic capacitor manufactured by aconventional method were also measured. As a result of this measurement,delamination was observed in the vicinity of the outlet portions for theexternal electrodes, that is, in the vicinity of the end surfaces of thesintered structure on which the external electrodes were formed. Thepercentage of the monolithic capacitors that had delamination was about25%.

The region of the monolithic capacitor according to this embodiment, inwhich the resist layer was formed, was observed by cutting the sinteredstructure. It was seen that the resist components disappeared and theBaTiO₃ components remained. Moreover, the portion in which the resistlayer had been formed was in a sintered state similar to the state ofthe other ceramic portions. Therefore, it can be considered thatsurrounding ceramics moved so as to replace the resist layer and,therefore, a dense sintered structure was formed.

Moreover, the first metal film 12 disappeared after the firing process.Therefore, although the first metal film is formed as described above,no short circuits are caused to occur in the monolithic capacitor thusobtained.

Second Embodiment

A multilayered ceramic substrate was manufactured by a method similar tothat according to the first embodiment except that a Cu film was used inplace of the Ag film to serve as the first metal film, an Ni film wasused in place of the Pd film to serve as the second metal film, resistresin containing 10 vol % of Al₂ O₃ powder and 5 vol % of glass powderwas used, and firing was performed at 1200° C. in a reducing atmosphere.

In the obtained multilayered ceramic substrate, there was no formationof a stepped portion between the portion in which the internalelectrodes overlapped one another, and the portion in which the internalelectrodes did not overlap.

The characteristics of the obtained multilayered ceramic substrate weremeasured. The desired design characteristics were attained. The obtainedmultilayered ceramic substrate was cut in the direction of itsthickness. No defect due to delamination was observed.

The region in which the resist was formed was in substantially the samesintered state as that of the other ceramic portions. That is, it can beconsidered that the resist components were evaporated, the containedglass components were dissolved, the alumina components were retainedand the surrounding ceramics were moved when the substrate was heatedfor sintering.

The copper components forming the first metal film substantiallydisappeared and, thus, no defects in terms of insulation or defects suchas generation of voids were seen to exist.

Third Embodiment

A monolithic capacitor was manufactured by a method similar to that ofthe first embodiment except that a resist was used to which no inorganicpowder, such as ceramic powder or glass powder, was added.

With this resist, the formation of a stepped portion between the portionin which the internal electrodes overlapped one another, and the portionin which the internal electrodes did not overlap, could not be reducedsatisfactorily. However, it was found that by applying pressureuniformly in the pressing process after the laminating step, it waspossible to satisfactorily prevent delamination, as compared with amonolithic capacitor obtained by the conventional method.

Although in the first to third embodiments the first metal film and thesecond metal film were formed of different metals, the same metal may beused to form the first metal film and the second metal film.

Fourth Embodiment

As shown in FIG. 8, a first supporting member 31 having the PET filmcoated with a silicon release agent (not shown) was prepared. On thesilicon release agent layer, there was formed the first metal film 32.The first metal film 32 was obtained by forming a Cu film having athickness of 0.1 μm on the entire surface of the first supporting member31 by an evaporating method.

Then, a resist layer 33 having a thickness of 0.8 μm was applied to thesurface of the first metal film 32, the resist layer containing 50 vol %of BaTiO₃ powder. Then, an exposing process and a developing processwere performed so that pattern holes 33a were formed in the resistlayer. As a result, a resist layer 33 having pattern holes 33a thereinas shown in FIG. 9 was formed.

Then, a second metal film 34 (see FIG. 10) was formed in each patternhole 33a. The second metal films 34 were obtained by forming Ni filmseach having a thickness of 0.8 μm by electroplating.

On the other hand, a second supporting member 39 comprising a PET filmhaving a thickness of 50 μm was prepared. Ceramic slurry, the maincomponent of which was BaTiO₃ powder, was formed on the secondsupporting member 39 in the form of a sheet, forming a ceramic greensheet 37.

Then, a roll-type press 35 was used on the ceramic green sheet as shownin FIG. 11 so as to transfer the metal-layer and resist-layer laminatedmember 36 (see FIG. 10) onto the ceramic green sheet 37 supported on thesecond supporting member 39. Then, the PET film 39 was stripped off. Asa result, a green sheet 38 which contains the above-mentioned metalfilms was formed.

Then, as shown in FIG. 12, a PET film was prepared as a third supportingmember 42, and the green sheets 38 were stacked on the third supportingmember 42 while their relative positions were accurately controlled.Whenever one green sheet 38 was stacked, heat pressing was performed.After each heat pressing process had been performed, the correspondingfirst supporting member 31 was stripped off so that a monolithicstructure was obtained, the obtained monolithic structure being shown inFIG. 12.

Then, the laminated member 41 obtained as described above was cut in thedirection of its thickness so that chips, each of which was formed intoa monolithic structure, were obtained to serve as individual monolithiccapacitors. Then, the monolithic chips were fired so that sinteredstructures were obtained, and then external electrodes were formedsimilarly to the first embodiment. As a result, monolithic capacitorswere produced.

Fifth Embodiment

A monolithic capacitor was manufactured similarly to the fourthembodiment except that resist containing no inorganic powder was used.

Evaluations of the Fourth and Fifth Embodiments

After performing the manufacturing process according to the fourthembodiment, the monolithic structure chip was cut to observe theinternal portion thereof prior to performing the firing process. It wasobserved that generation of a stepped portion between the portion inwhich the second metal films forming the internal electrodes overlappedone another and other portions could substantially be prevented.

Sintered structures in the obtained monolithic capacitor were cut in adirection parallel to the end surface on which the external electrodeswas formed so that the internal structure was observed. It was observedthat generation of a stepped portion between the portion in which theinternal electrodes overlapped one another and the portion in which theinternal electrodes did not overlap was substantially prevented. Thatis, the structure in which ceramic powder was contained in the resistlayer prevented generation of the stepped portion at the time ofperforming the firing process.

In the portion in which the resist layer was formed, resin contained inthe resist disappeared and the contained ceramic powder was retained.Moreover, the structure of the portion of the sintered body in whichresin initially existed was substantially the same as that of the otherceramic portions. Therefore, it can be considered that the ceramicpowder retained and the surrounding ceramics moved at the time ofperforming the firing process so that a structure of the portion thatoriginally contained resin became the same as that of the surroundingportion.

Moreover, probably due to the thickness of the first metal film, towhich the resist was applied, of 0.1 μm or thinner, the first metal filmwas changed into an insulating structure due to the firing process.Therefore, it can be understood that monolithic capacitors can stably besupplied, which do not easily encounter defects, such as short circuits,defective insulation, generation of voids and delamination.

Also, after carrying out the process of the fifth embodiment, themonolithic chip was cut in the direction of its thickness prior toobtaining the sintered structure to observe the stepped portion, betweenthe portion in which the second metal films forming the internalelectrodes overlapped one another, and the other portions. Although thestepped portion was not significantly reduced as compared with themonolithic chip obtained in the fourth embodiment, the stepped portionwas reduced satisfactorily as compared with the monolithic chip obtainedby the conventional method.

The internal structure of the obtained sintered structure was analyzedsimilarly to the evaluation method employed in the fourth embodiment. Itwas seen that the first metal film portion was converted into aninsulating structure due to the firing process. Moreover, the obtainedmonolithic capacitor was free from defects, such as short circuits,defective insulation, generation of voids and delamination.

In the manufacturing methods according to the fourth and fifthembodiments, only the ceramic green sheet was in contact with thesupporting film. Therefore, the release agent layer on the film is onlyrequired to enable the ceramic green sheet to be stripped easily. Thus,an appropriate release agent on the market can be employed and,therefore, the release agent layer can easily be designed.

The force required to strip off the supporting film when the layers werestacked in the case where an appropriate release agent layer wasemployed was measured. Results are shown in Table 1.

                  TABLE 1                                                         ______________________________________                                                      Force required to                                                             strip a supporting film                                         ______________________________________                                        Conventional Structure                                                                        20 g/cm.sup.2                                                 Embodiments 4 and 5                                                                            3 g/cm.sup.2                                                 ______________________________________                                    

As can be understood from Table 1, the supporting film could be strippedfrom the ceramic green sheets according to the fourth and fifthembodiments with a force that was one-third that required with theconventional structure. Therefore, a problem of defective transferencecan satisfactorily be prevented and, thus, generation of delaminationcan significantly be prevented.

The following embodiments are additional examples, in each of which thepresent invention is adapted to manufacture a monolithic capacitor. Thefollowing processes, including the process for obtaining the monolithicceramic structure which has not been fired, employ a mother multilayeredmetal film and a mother ceramic green sheet.

Sixth Embodiment

As shown in FIG. 13(a), a polyethylene terephthalate (PET) film wasprepared serving as the first supporting member 111. The top surface ofthe first supporting member 111 was coated with silicon resin (notshown). A first metal film 112 was formed thereon. The first metal film112 could be obtained by forming an Ag film having a thickness of 70 nmon the entire surface of the first supporting member 111 by anevaporation method. Then, a resist layer having a thickness of 1 μm isapplied to the top surface of the first metal film 112, and thenexposing and developing processes are performed. As a result, a resistlayer 113 patterned as shown in FIG. 13(b) is formed. Next, a secondmetal film 114 is formed in each of the pattern holes 113a of the resistlayer 113 by a thin film forming method. In this embodiment, the secondmetal film 114 is formed to have a thickness of 0.5 μm by electroplatingPd.

Then, the resist layer 113 is stripped off by using resist strippingliquid or the like. Thus, a multilayered metal film 115 shown in FIG. 14is obtained, the multilayered metal film 115 including the second metalfilm 114 formed on part of the first metal film 112. The multilayeredmetal film 115 is in contact with the first supporting member 111 ononly the lower surface of the first metal film 112. As a result, thereleasing layer on the PET film is only required with respect toreleasing the first metal film 112. Therefore, the releasing layer onthe top surface of the PET film can easily be designed.

The second metal film 114 corresponds to the portion to be finally usedas the internal electrode, while the first metal film 112 is to bechanged into an insulating structure due to a process to be describedlater.

Next, a ceramic green sheet 116 is formed on the multilayered metal film115. In this embodiment, ceramic slurry is formed into a sheet having athickness of 8 μm by a microgravure method so that a ceramic green sheet116 is formed (see FIG. 15).

As shown in FIG. 15, by forming the ceramic green sheet 116, a greensheet 117 having the above-mentioned metal films is prepared while beingsupported on the PET film 111.

Then, the green sheets 117 are sequentially stacked so that a motherlaminated structure 118 shown in FIG. 16 is obtained. Although FIG. 16shows two of the green sheets 117 in the laminated structure 118,additional such green sheets 117 may be further stacked in the upwarddirection. Reference numeral 119 represents a supporting film for use inthe laminating process.

The mother laminated structure 118 is cut in a direction of itsthickness to be formed into individual monolithic ceramic structures forrespective monolithic capacitors. Thus, monolithic ceramic structuresfor respective monolithic capacitors are obtained.

The monolithic ceramic structures are fired at 1200° C. for 4 hours inthe atmosphere. In the firing process, the first metal film 112 isconverted into an insulating structure at the same time as the non-firedceramics are fired. That is, metal components forming the first metalfilm 112 are changed into oxide ions which are diffused into thesurrounding ceramics so as to be changed into insulating substances.Therefore, only the internal electrodes formed by the second metal films114 remain in a final sintered structure 120, the cross sectional shapeof which is shown in FIG. 17. Although FIG. 17 shows only two secondmetal films 114, a multiplicity of additional second metal films 114serving as the internal electrodes overlap one another in the upwarddirection with ceramic layers being interposed between them.

By forming a pair of external electrodes on the two end surfaces of thesintered structure 120, a monolithic capacitor 121 shown in FIG. 18 isobtained. In the monolithic capacitor 121, a plurality of the internalelectrodes formed by the second metal films 114 overlap one another inthe sintered structure 120. Sintered ceramic material intervenes betweenthe internal electrodes. Note that reference numerals 122a and 122brepresent external electrodes. The external electrodes 122a and 122b canbe formed by any appropriate method, such as applying, firing or platingof conductive paste.

The generation of a stepped portion in the thus-obtained monolithiccapacitor, between a portion in which the internal electrodes overlappedone another, and a portion in which the internal electrodes did notoverlap, was examined. It was found that the stepped portion can bereduced by a quantity obtainable by calculating (the thickness of thefirst metal film)×(the number of stacked first metal films).

Twenty monolithic capacitors were prepared, and each of the monolithiccapacitors was cut in such a manner that its cross-section is exposed tothe outside as shown in FIG. 18 to observe whether or not delaminationhas taken place. No delamination was observed. Similarly, twentymonolithic capacitors were cut in such a manner that theircross-sections perpendicular to the cross-section shown in FIG. 18 wereexposed to the outside. Again, no delamination was observed.

By comparison, it was observed that delamination had taken place in fivemonolithic capacitors out of every twenty monolithic capacitors obtainedby the first method described above as related background art. Thecross-sections observed were in the same directions as thecross-sections shown in FIG. 18.

Since the fusing point of the first metal film was about 960° C., whichwas a sufficiently low level with respect to the sintering temperatureof 1200° C., the first metal film was formed into the insulatingstructure. Therefore, the monolithic capacitors according to theembodiment were free from short circuits.

Seventh Embodiment

Similarly to the sixth embodiment, monolithic capacitors weremanufactured, except that the first metal film was made of Cu and thesecond metal film was made of Ni. The ceramic slurry was composed ofBaTiO₃ -type ceramics which did not contain Cu. The firing process wasperformed with the partial pressure of oxygen set to a level at whichthe plated Ni film could not be oxidized, but at which the evaporated Cufilm could be oxidized, during the initial period of the firing process,that is, half of the period during which the temperature for firing wasmaintained at the highest level. Specifically, the partial pressure ofoxygen was set to 10⁻⁴ Pa. After the initial period of the firingprocess had been performed at the partial pressure of oxygen of 10⁻⁴ Pa,the firing process was performed in a reducing atmosphere. The otherconditions were the same as those employed in the sixth embodiment sothat the monolithic capacitors were manufactured.

The sintered structure of each of the monolithic capacitors obtained inthe seventh embodiment was analyzed. Uniform distribution of Cu in theceramics was confirmed. That is, diffusion of Cu composing the firstmetal film in the ceramics was confirmed.

The electrical characteristics of the obtained monolithic capacitorswere measured. As a result, an effect similar to that obtainable in thecase where Cu powder was added to BaTiO₃ -type ceramics could beobtained.

The cross-section of each monolithic capacitor was observed similarly tothe sixth embodiment. No generation of delamination was observed.

Although in the seventh embodiment, the partial pressure of oxygen wascontrolled in the initial period of the firing process to diffuse Cucomposing the first metal film, an oxidation diffusing agent may beadded to the first metal film or a diffusion enhancer may be added todiffuse the metal components composing the first metal film into theceramics.

Eighth Embodiment

As shown in FIG. 19, a PET film serving as the second supporting member131 is prepared. The top surface of the PET film 131 is coated withsilicon resin (not shown).

By forming ceramic slurry on the PET film 131 by a doctor blade methodand then drying it, a ceramic green sheet 132 having a thickness of 8 μmis formed.

On the other hand, a PET film shown in FIG. 20 is prepared as the firstsupporting member 133. The top surface of the PET film 133 is coatedwith silicon resin (not shown).

Similarly to the sixth embodiment, a first metal film 134 and a secondmetal film 135 are formed on the PET film 133. In this embodiment, thefirst metal film 134 is made of Ag and the second metal film 135 is madeof Pd. Thus, a multilayered metal film 136 is formed.

Then, a calender roll 137 is used as shown in FIG. 21 to transfer themultilayered metal film 136 to the ceramic green sheet 132. Then, thePET film 131 is stripped off so that a green sheet 138 integrally havingthe metal film 136 as shown in FIG. 22 is obtained.

By stacking the thus-obtained green sheets 138, a laminated structurecan be obtained. That is, by stripping and stacking the PET films 133while transferring the green sheets 138, a monolithic ceramic structuresimilar to that obtained in the sixth embodiment can be obtained.

The thus-obtained monolithic ceramic structures were used to manufacturemonolithic capacitors similarly to the sixth embodiment.

An observation was performed as to whether or not the obtainedmonolithic capacitors according to the eighth embodiment encountereddelamination. No generation of delamination was observed.

Since the method of manufacturing a monolithic capacitor employing theconventional transferring method involves the ceramics and the metalfilm being in contact with the supporting film, the supporting film mustbe easily stripped from both of the ceramics and the metal film.However, since the eighth embodiment has the structure in which only thefirst metal film 134 is in contact with the PET film 133, the PET film133 is required to be easily stripped from only the first metal film134.

In the sixth to eighth embodiments, the first metal films 112 and 134are partially diffused in the firing process and, therefore, they arechanged into insulating structures. As a result, it can be understoodthat a complicated process is not required in which the first metal filmportion, which is not located below the second metal film, is strippedby etching or the like.

Although the sixth to eighth embodiments have the arrangement in whichthe first metal film is made of Ag or Cu and the second metal film ismade of Pd or Ni, other metals may be employed if the effect of thepresent invention can be attained.

Although the invention has been described in its preferred form with acertain degree of particularity, it is understood that the presentdisclosure of the preferred form can be changed in the details ofconstruction and in the combination and arrangement of parts withoutdeparting from the spirit and the scope of the invention as hereinafterclaimed.

What is claimed is:
 1. A method of manufacturing a monolithic ceramicelectronic device comprising the steps of:forming a first metal film onsubstantially all of one major surface of a first supporting member by athin film forming method; forming a multilayered metal film by forming asecond metal film on a part of said first metal film by a thin filmforming method; wherein said second metal film is thicker than saidfirst metal film; forming a monolithic ceramic structure incorporatingsaid multilayered metal film; and changing a portion of said first metalfilm, which is not overlain by said second metal film in said monolithicceramic structure, into an insulating material in such a manner thatmetal components forming said portion are diffused into the ceramics,while firing said ceramics.
 2. A method of manufacturing a monolithicceramic electronic device according to claim 1, wherein the thickness ofsaid first metal film is 100 nm or less and the thickness of said secondmetal film is at least 300 nm and at most 1000 nm.
 3. A method ofmanufacturing a monolithic ceramic electronic device according to claim1, wherein said step of changing said portion of said first metal filminto the insulating material while firing said ceramics is performed byfiring said monolithic ceramic structure under a partial pressure ofoxygen at which said first metal film is oxidized but said second metalfilm is not oxidized.
 4. A method of manufacturing a monolithic ceramicelectronic device according to claim 1, wherein said step of formingsaid multilayered metal film includes the steps of:forming, on saidfirst metal film, a resist layer having pattern holes therein; forming,within each of said pattern holes in said resist layer, a second metalfilm which is thicker than said first metal film by a thin film formingmethod; and stripping off said resist layer.
 5. A method ofmanufacturing a monolithic ceramic electronic device according to claim1, wherein said step of forming said monolithic ceramic structureincludes the steps of:forming a green sheet containing a metal film byforming a ceramic green sheet on said multilayered metal film; andstacking a plurality of said green sheets.
 6. A method of manufacturinga monolithic ceramic electronic device according to claim 1, whereinsaid step of forming said monolithic ceramic structure includes thesteps of:forming a ceramic green sheet on a second supporting member;forming a green sheet containing a metal film by transferring, to saidceramic green sheet, said multilayered metal film supported by saidfirst supporting member; and forming a monolithic ceramic structure bysequentially transferring a plurality of said green sheets.
 7. A methodof manufacturing a monolithic ceramic electronic device according toclaim 6, wherein said multilayered metal film is transferred to saidceramic green sheet by using a roll press.
 8. The method ofmanufacturing a monolithic ceramic electronic device according to claim1 wherein a partial pressure of O₂ is maintained in said changing stepso that said first metal film is oxidized while the second metal film isnot oxidized, during a first partial period of said changing step. 9.The method of manufacturing a monolithic ceramic electronic deviceaccording to claim 8, wherein said first metal film includes Cu and thesecond metal film includes Ni.
 10. The method of manufacturing amonolithic ceramic electronic device according to claim 9, wherein saidpartial pressure of O₂ is about 10⁻⁴ Pascal.
 11. The method ofmanufacturing a monolithic ceramic electronic device according to claim8, wherein the changing step is performed under reducing conditionsduring a second partial period of said changing step.